1. Field of the Invention
The invention disclosed in this specification relates to semiconductor devices.
Note that a semiconductor device in this specification and the like refers to any device that can function by utilizing semiconductor characteristics, and semiconductor elements, electro-optical devices, storage devices, signal processing units, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
The configurations of semiconductor integrated circuits typified by LSIs are fixed at the time of manufacture and cannot be generally changed after manufacture. In contrast, in semiconductor integrated circuits called programmable logic devices (PLDs), a logic block composed of a plurality of logic circuits is considered as a unit and logic blocks are electrically connected to each other through wirings. In a programmable logic device, the circuit configuration of each logic block can be electrically controlled.
As above, the design of a programmable logic device can be changed after manufacture; thus, the use of a programmable logic device can drastically reduce the time and costs needed to design and develop semiconductor integrated circuits.
There are some programmable logic devices called complex PLD (CPLD) and field programmable gate array (FPGA). In either device, the circuit configuration of each logic block is controlled by a programmable switch that is switched in accordance with data (configuration data) stored in a memory unit provided in the logic block. In other words, programming data into each programmable switch makes it possible to change the circuit configuration of a programmable logic device.
Volatile memory such as SRAM is used as the memory unit. On the other hand, for example, Patent Document 1 discloses a technique for using nonvolatile memory composed of a floating gate transistor, such as flash memory, as the memory unit.
In addition, a programmable analog circuit having an array composed of functional units including analog elements has been developed.